Fix message when step is canceled through TestContext

[Evangelink]

Improve error message when step (fixture or test method) is being cancelled through the TestContext.

Before for AssemblyInitialize:

Assembly Initialization method Playground.TestClass.AssemblyInitialize threw exception. System.OperationCanceledException: The operation was canceled.

After for AssemblyInitialize:

Assembly initialize method 'UnitTest1.AssemblyInitialize' was canceled